No. 242.

LONDON, SATURDAY, APRIL 19. [1827-8.

LECTURES ON CHEMISTRY,

BY

PROFESSOR BRANDE.

Delivered at the Royal Institution of GreatBritain.

LECTURE XXXVIII.

On Bismuth, Uranium, Titaniu7it, Cerium, Tel.luriu.m, Selenitim, and Arsenic, and theircompounds.

1 addition to the uses of the oxide of co-balt as a colouring matter for porcelain andglass, it is used largely in the paper manu-factories to cover the yellow tinge whichit would otherwise exhibit ; and the quan-tity of cobalt is so considerable in some pa-per, that, when it is burnt, the ashes are of ablue colour. In the manufacture of starch, itis also customary to use a little cobalt, to giveit a pale blue tint, which covers the yellow,and renders the whole of a whiter hue.

Bismuth is a metal not of any considerableimportance ; it occurs native, combined witharsenic and cobalt. Like antimony, it is ofa brittle white colour, easily crystallisable,and is one of the best with which to per-form the experiment of crystallising metals :it is very fusible, and very combustible. Ifheated upon charcoal with oxygen, it melts,burns with a bluish flame, and gives out aquantity of a dense vapour, which is oxideof bismuth. We show you this experiment,because you might not otherwise be awareof the extreme combustibility of the metals.The yellow fumes thrown off are the oxide ofbismuth, and I should state, that the tempe-rature at which it fuses is about 500° ofFahrenheit.The composition of its oxide is 71 bis-

muth, aud 8 oxygen, or one proportionaland one ; and it may be formed in variousother modes than that just shown you,namely, by dissolving bismuth in nitricacid, precipitating the solution by pouring

it into water, and by washing the preci-pitate with an alkali, which gives me an op-portunity of showing you another very im-portant character of the salts of bismuth,namely, that they are decomposed andprecipitated by pure water. You cannot,therefore, dilute a nitrate or muriate of bis-muth to any extent, without precipitatingthe oxide. Here, you observe, I act uponthe crystallised nitrate of bismuth ; the saltis decomposed in, not dissolved by, the wa-ter, and a subnitrate of bismuth is throwndown. Now if vou add an alkaline solutionto the subnitrate, and wash it thoroughly,you obtain the oxide of bismuth, a white im-palpable powder, known formerly under thename of blanc defard and blanc de perle, orpearl white, and magistery of bismuth, andwas much used as a cosmetic by the Frenchladies ; but it was soon found that the pre-paration was apt to become black on expo-sure to certain agencies, and that a lady sit-ting by a large fire, had one cheek brown ortawny, whilst the other was white and pink,the cheek next the fire changing colour bythe escape of a little sulphurous vapour.Sulphuretted hydrogen does the same thingwith the oxide of bismuth as with whitelead ; it soon discolours it, therefore it isnot fitted to become a pigment.The action of chlorine upon bismuth pro-

duces nothing particularly interesting; itis usually made by heating the metal inchlorine, or by dissolving it in corrosive sub-limate ; it runs down in an oily kind of fluid,called butler of bisrwath. A very curious pro-perty of bismuth is, that it renders othermetals very fusible when alloyed with it.If you mix together equal parts of bismuth,lead, and tin, you obtain a very fusible me-tal ; lead and tin alone are very fusible, butnot so much so as when mixed with the bis-muth. The proportions generally used to

form the alloy called Sir Isaac Newton’sfusible metal, is a mixture of eight partsbismuth, five of lead, and three of tin. You

may alter the proportions of lead and tin,without altering its fusible property, but itis necessary that the bismuth should con-stitute about half of the alloy. It is so fusi-ble, you observe, that on bringing it into thevapour of boiling water, or dipping into wa-

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ter nearly boiling, it readily melts down.Tea spoons are sometimes made of this alloy,which are neatly polished, and sold for

amusement, being fusible at a heat a littlebelow 212. The addition of a little mercuryto the alloy renders it still more fusible,but at the same time so brittle as to be in

danger of breaking. I do not know that this

alloy has been extensively used, but it hasbeen proposed as a soft plug for the steamboiler, in such proportions as to melt a littleabove the boiling point; but there are so

many other better modes of effecting thispurpose, that it is not probable it will beresorted to.We now come to a set of metals which

we shall pass very hastily over, since theyare applied to no use in the arts, in medi-cine, or in analytical or experimental che-mistry. One or two of them exhibit somecurious properties, and it would notbe rightto pass them over entirely in silence.

Uranium is met with in several states

native, but chiefly in the state of oxide, ofwhich you see a specimen here ; it was for-merly called pech blende, and was first ana..lised by Klaproth, who showed it to be a

hydrated oxide of uranium, containing alsoa little copper. The salts which this oxideforms when in solution, are of a yellow co-lour, of which you see some specimens onthe table. Here is the hydrated oxide, thechloride, the nitrate, all of a yellow colour ;the sulphate is more of a green tint. Fromall these solutions of uranium, you may ob-tain the precipitation of the oxide by analkali. The metal is distinguished from allothers by this characteristic, and by thebeautiful red colour, or reddish brown colourof the precipitate furnished by the ferrocya-nate of potash. There are some other pre-parations of uranium, which you may exa-mine, ifvou choose, after the lecture. Thenumber representing uranium is about 26 or27 upon Dr. Thomson’s list. I have not

given you a tabular view of the compoundsof uranium, because they have really beentoo little examined to speak with any cer-tainty respecting them. The specific gra-vity of the metal is 9.

Titaninm is a metal found nearly pure inthe state of oxide in a mineral called titan-ite; it is also met with combined with ox-ide of iron, and in the peculiar substancewhich you see here, found by Mr. Gregororiginally in the vale of Menachan, in

Cornwall, and hence called ?neriachanite.The metal is so intractable and so diffi-cult of fusion, that had it not been foundin the metallic state, it would appear doubt-ful whether it ever existed in that state. Itwas discovered by Dr. Wollaston, that inthe slag of some iron mines there was a veryhard insoluble infusible incrustation, which,by examining further, was proved to be ti.

tanium in a state of purity, or nearly so. If

you digest it in nitro-muriatic acid, you willseparate almost every thing from the titan.ium, and by digesting it in this way, youobtain a brittle greyish metal; and the

only way of oxidising it, is to treat it alter-

nately with nitre and borax ; the nitre oxi.dises it, and the borax dissolves some ofthe oxide. By fusing it with a carbonatedalkali, it is acted upon slowly, and if youfuse menachanite with a carbonate of potash,

and wash off the alkali with an acid, you ob.I tain a carbonate of titanium. It is the hardestmetal known : it scratches rock crystal, andmav be said to be infusible.

Cerium is a metal obtained from allanite,a Greenland mica. It was obtained byBerzelius from a mineral found in Sweden,and whic4 he called cerite. It is of a yellowcolour, and so are all its salts; but I shallnot detain you with them, as they are of i3oimportance. Here are specimens of themuriate, sulphate, carbonate, and so on.

Tellurium is found native, alloyed withiron and gold ; and is represented by thenumber 38. It is characterised by its readyfusibility, great combustibility, and by being 0soluble in hydrogen, forming a tellurettedhl/d1’oeen ,B’tM.

Selenium.-Under the head sulphur, Imentioned to you, that in examining pyrites,Berzelius discovered a singular substance,capable of entering into a variety of com.pounds, and he was disposed to regard it asa primitive body ; but I then informed you,it seemed rather to belong to the simple com-bustible bodies, than to the metals. Itseems to rank more with sulphur and ptios-phorus, and substances of that description,than with the metals.

Arsenic.-This then brings us to the sub.

ject of arsenic ; as a metal, it is not appliedto any very important purposes, and is onewhich we could very well do without. Ithas been employed in medicine, and derivesits principal interest to the chemist from itspoisonous qualities, and consequently thechemist is called upon to ascertain its exist.ence in combination with other substances.

I shall endeavour to give you a briefaccount of some of the principal combinationsof arsenic, and afterwards show you thesimplest modes of detecting it.! Now, with regard to the ores of arsenic;they are very numerous, and you have al-ready seen it as existing in copper ore,which often contains it in large quantities,and from which, and other ores, it is easilyliberated by the application of heat. Hereis an ore of arsenic, called arsenlcal pynts,it being a sulphuret of iron and arsenic.-Here is another ore, in which the arsenicis nearly in a state of purity. From any ofthese sources, whether from its own properore, or from its compounds with the other

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metals, it is collected by sublimation, andhaving undergone a second sublimation topurifv it, it is brought into the market un-der the name of white arsenic. Althoughsometimes nearly transparent, and like

glass, it becomes opaque and pulverulenton exposure to air. If you mix white arse-nic with a small quantity of potash andcharcoal, and apply heat, as has been donein this tube, a steel-grey substance will

rise, which is the metallic arsenic in a stateof purity. The use of the potash is to

keep down the arsenic at a red heat, thecharcoal combining with the oxygen of thewhite arsenic, and the metallic arsenic issublimed and carried to the top of the tube ;and this is often the only way in which wecan satisfactorily detect the presence of themetal. A very small quantity of the whitearsenic would suffice for this process ;half a grain put into a small glass tube,touched with a drop of the carbonate ofpotash, and the least drop of oil, or anyother carbonaceous matter, would, on theapplication of heat, afford a decided metal-lic sublimation of a steel-grey colour. Themetal is so volatile that it volatilises before itfuses, and its oxide is more soluble in hot thanin cold water, and accordingly we find, thatthe native ores of arsenic are soluble ; someof these are sold under the name offiy-stones,being boiled in water, to which sugar isafterwards added for these insects. At a

temperature of 360 it rises in vapour, butits point of fusion is not readily determined,because it so easily passes into vapour thatit is difficult to fuse even under pressure.When heated upon a platinum spoon, it

goes readily into vapour, burning with ablue flame, and it renders the platinum,which is of itself difficult of fusion, sofusible that a hole is generally made init, through which the arsenic runs. Theheated vapour is characterised by a peculiarsmell, which, when once perceived, cannotbe mistaken ; it is like the smell of garlicand is most poisonous, and the miners whowork where the ores of arsenic abound,generally suffer from paralysis, and othernervous affections. By this simple processof combustion, the metal passes into the stateof a white oxide of arsenic, or arsenious acid, asit has been sometimes called, inasmuch asit enters into combination with certain ofthe metals, after the manner of an acidand constitutes a class of salts called arse-nites. The number representing arsenic is38 ; and the white arsenic,or arsenious acid,isa compound of one proportional of metal 38,and two of oxygen 16, giving the equivalent54. Such, then, is the composition of thewhite arsenic ; that it is virulently poison-ous I need scarcely remind you, or that thesymptoms which it produces are inflamma-tion of the stomach and fauces; not that

inflammation is of itself sufficient to accountfor the rapid death it produces, as it is

equally poisonous when applied to a wound,and, what is curious, the same symptomswill be produced in the stomach as we sus-pect to be the consequence of the contactof arsenic with that viscus. If you heatarsenic very slowly, so that it may rise invapour, it crystallises in transparent octae-dra, as you see here. With regard to itssolubility in water, it has been variouslystated, but we shall be pretty correct insaying, that 1000 parts of water at 60° dis-solve l2 parts of the white oxide ; at ’i!129the same quantity of water will take up 77parts of the oxide, and will retain as muchas 30 parts in solution when cold. It isvolatile at 380°, and its smell is exceedinglypeculiar and alliaceous ; but it has beenshown bv Dr. Paris, and others, that, whenheated carefully, out of the contact of anysubstance that can decompose it, it rises inan inodorous vaptur. In heating the arsenic,if you hold it upon glass, taking care thatthe name of the lamp comes no where incontact with the arsenic, it would rise in awhite inodorous vapour ; but the carbonaceous matter of the lamp acts upon thewhite arsenic, decomposes a portion of it,evolving a little metallic arsenic, and it isthe metallic arsenic only which, it is said,has the alliaceous odour. It is of import-ance to settle this point in your minds,because, if you should heat it in a waywhich prevents the decomposition of thewhite arsenic, you might be led to suspectthat no arsenic was present, in consequenceof the absence of the garlio smell ; but youmust be careful to try it with other tests.The taste of arsenic is singularly nauseous ;it creates a peculiar astringent sensationabout the mouth and fauces, a great flow ofsaliva, and a painful feeling in the mouth,which can never be forgotten by those whohave made the experiment; it is certainlynot a very pleasant thing to take into themouth, but it is worth while to try it foronce, to take a taste. It reddens vegetableblues, and has been called arsenious acid,properly enough, as it forms a distinct setof salts. With ammonia, potash, and sodait forms, as you see here, soluble compounds,which are arsenites of these substances.One of these, the arsenite rf potash, is usedin pharmacy, under the name of Fowler’smineral solution, and the liquor arsenicalis of .

the present pharmacopoeia, is a solution of it.At one time it gained great celebrity in thecure of agues, and there can be no doubtthat it will cure obstinate ague ; but, at thesame time, it is such a dangerous substance,and there are so many other medicineswhich answer equally well, that it ought tobe prohibited altogether, and no longer usedin pharmacy. With regard to its boasted

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cure of agues, my opinion is, that they wouldyield equally to the sulphates of zinc, cop-per, or quinine, and it should be altogetherprohibited from commerce, and that wouldbe the only way of preventing the fatalresults so frequently attending its use.

I shall not go through a description of allthe arsenites, but such only as may be em-ployed in the detection of the metal. Thearsenite of silver may be easily made by dou-ble decomposition, by adding to a solutionof nitrate of silver a solution of arsenite of

potash. You observe, that on mixing thetwo solutions, the arsenite of silver fallsdown in a yellow cloudy precipitate, which isvery characteristic of the presence of arse-nic ; and although phosphate of silver occa-sionally assumes a similar appearance, stillthat is not to interfere with your usingnitrate of silver as a test of the presence ofarsenic. There is a mode of applying thistest which is useful sometimes in determin-

ing the presence of arsenic, which consistsin forming a very dilute solution of arseniteof ammonia. Suppose you have a suspectedsubstance, heat it with a little solution ofammonia, and then dilute the solution veryconsiderably, dip a stick of the nitrate ofsilver into it, and you immediately observethe arsenite of silver falling from it, as a

decided yellow precipitate. This test was

suggested by Mr. Hume, of Longacre. Yousaw what a very minute quantity of thenitrate of silver came in contact with thefluid, and how evident the presence of arse-nic is rendered. You must remember thatthis test is soluble in ammonia, and of con-sequence that it is very easy to dissolvethe precipitate; and if you now apply ni-trate of silver to this solution containingarsenic, you will have no longer a preci-pitate produced. Whenever, therefore, youuse nitrate of silver, take care that no ex-cess of ammonia, or any foreign matter, bepresent, and then the yellow appearance ofthe arsenite of silver is very characteristicof the appearance of arsenic.The arsenite nf’ copper may be made by i

double decomposition, by adding a littlesulphate of copper to a solution of the arse-nite of potash ; the precipitate is of an applegreen colow’. This was formerly called:Scheele’s green, which is, in fact, an arse-nite of copper, and its green colour is oftenresorted to as a test of the presence ofarsenic.When white arsenic is heated with ni-

tric acid, it decomposes the acid, absorbspart of its oxygen, and is converted into a

deliquescent white substance, or arsenicoxidised to its maximum, composed of threeproportionals of oxygen H4, and one ofmetal S8, giving 6S as its equivalent ; it issour to the taste, and is much more solublethan white arsenic; and this compound is the

arsenic acid. It enters into combination withvarious bases, and forms a class of salts some-times used in medicine. With potash itforms an uncrystallisable salt, but with twoproportionals of acid it forms a binarseniate

of potash, which is very soluble. It used tobe called Macque:)"s tasteless agne salt. Thearseniate of soda is a crystallisable salt. Thearseniate of lime is very difficultly soluble ;and you see specimens of arseniates ofbaryta, strontia, magnesia, and so on, onthe table. Now, these arseniates are prin.cipally interesting as entering into manynative combinations with copper, lead, andother metals, some of which are very beau.tiful.

Chlorine and arsenic combine and producea compound, long known under the nameof butter of arsenic ; it is not an importantcompound, but it is obtained by distillingarsenic with corrosive sublimate ; it is com-

posed of one proportional 38, and two pro.portionals of chlorine 72, so that its equi-valent is 110. Iodine and arsenic combine,and produce an iodide of arsenic ; and arse-nic and sulphur combine to produce a sut.phuret of arsenic, which has been found na.tive in the ore called orpiment or realgar.Orpiment is sometimes beautifully lamel.lated, and it produces a fine yellow colour,which has been used as a paint, but it is

objectionable on account of its highly poison-ous quality.Now, if you add a hydro-sulphuret of

ammonia to a solution of arsenic, you get,under particular circumstances, a yellow pre.cipitate ; and sulph1Lretted hydrogen has beenparticularly recommended as a delicate testof arsenic. I shall show you how far thisis to be depended on. Here is a solutionof white arsenic in water, which I shall di-lute very considerably, and then add to ita little sulphuretted hydrogen dissolved inwater. (This experiment was made.) Youobserve that you are far from getting a de.cided change of colour, or precipitation,sufficient to discover the presence of arse’nic. If you add a solution of the gas in

larger quantities you will get a yellow co’lour, and ultimately a yellow precipitate,but it is not a test altogether to be depend.ed upon. By adding hydrosulphurets ofammonia, or potash, to solutions containingarsenic, you get similar results.Now there remain one or two points for

our consideration in connexion with arsenic,and we shall reserve them for the next lec’ture ; but, before we separate, I wish to

call your attention to the properties of arse-naeretted hydrogen gas. The mode of obtain-ing this gas is very simple : put into a flasksome zinc filings, water, sulphuric acid, andwhite arsenic. Hydrogen gas is rapidlyevolved, and during the evolution of thegas it acts upon and decomposes the white

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arsenic, and carries off a certain quantity ofmetallic arsenic in solution. Now here youhave this gas, and it is one of the most

poisonous compounds that you can imagineto exist, because it contains a large quan-tity of arsenic, and that in the most diffu-sable of all possible forms, namely, thegaseous. You see that a quantity of thewhite fumes of the oxide of arsenic is libe-rated, that a portion of hydruret of arsenicis liberated, and that the gas burns with ablue flame ; it contains a considerable quan-tity of arsenic dissolved in the hydrogen.It is easily decomposable by chlorine, andconsequently where it exists chlorine willact as a disinfector.The other modes to be resorted to for de-

tecting the presence of arsenic, where it is

suspected, I shall show you in the nextlecture, but I shall not enter into veryminute details, and I shall give you my rea.sons for not doing so. I conceive, that unlessthe evidence is very clear and decided, weought not to be satisfied with the veryminute and refined chemical investigationswhich have often been served up in courts Iof justice in cases of this kind. i

FOREIGN DEPARTMENT.

EXPERIMENTS ON THE SECRETION OF BILE,

BY M. SIMON DE METZ.

THE secretion of bile is an interestingpoint of physiology, on which considerableuncertainty prevails, on account of thedifficulties which present themselves to

those who have undertaken to develop itsmechanism. Is the bile derived from arte-rial blood, in the same way as the othersecretions are produced, or from the bloodof the vena porta ? or, do both arterial andvenous blood contribute to its formation?Such are the questions which have for along time agitated the profession, and forthe solution of which I have made a greatnumber of experiments, which appear tothrow considerable light on this subject.

It has been stated, that it is very diffi-cult, if not almost impracticable, to put li-gatures on the vessels of the liver ; but Ihave observed that the difficulty depends onthe kind and age of the animal on which theexperiment is made. Thus, for instance,what has been deemed not feasible on dogs,has been tried with satisfactory results onrabbits and pigeons. In these two differentanimals I have succeeded in tying the celiac,or the hepatic artery, or the vena porta, orthe excretory duct ; and the interruption ofths passage of the fluids ia these different

vessels has given rise to different results’i Pigeons, as it is well known, have no gall; bladder, but they have two hepatic ducts,the one from which the bile flows almost

continuously, and opens near the gesier;the other, which is often found empty, islonger and thinner, and opens further intothe small intestines. The trunk of the he-

patic artery has a very small diameter, andis deeply situated, so that it is difficult topass a ligature on it ; nevertheless it is pos-sible to reach it by employing small curvedneedles conducted by means of the forceps.

1. If the two hepatic ducts of these ani-mals be tied whilst the bile continues to flow,the liver becomes engorged, and filled withglobules of a fine green colour, which arediffused principally on the surface of the

organ. The neighbouring part, the peri-cardium, the omentum, and intestines arecoloured by them. The animals generallysurvive from twenty-four to thirty-six hoursafter the experiment.Between ten and twenty hours after the

application of the ligature, an importantphenomenon presents itself. The animal

discharges at these periods, fosces which arequite green, and of the same colour as thebile with which the liver is engorged. Thisdiscoloration of the fasces increases up to thetime of death. I first thought (the naturalexcretory passage being intercepted by theligature) that the bile was absorbed intothe liver, then excreted into the intestines,and mixed with the secretions of the ali-

mentary canal. But I soon succeeded in

positively ascertaining that this green mat-ter was only to be found in the cloaca, whereit was carried by the ureters, and that theintestines contained no trace of it, except-ing in the inferior part of the rectum, whereit had accumulated. MM. Dumas and Pre-vost have remarked, that the secretion ofthe bile is augmented by the interruption ofthat of the urine. Hence we see the secre-tion of urine effects an outlet for the elimi-nation of the bile, which in the naturalcourse had been prevented; thus proving,that the liver and kidney are more or lessdependent on each other.

2. Ligatitre of the Excretory Ducts, andHepatic Artery.-Twelve hours after these

ligatures had been applied, the surface ofthe liver, as well as the neighbouring parts,attained a yellowish tins, the ducts were

gorged, and announced the presence ofbile. Twenty hours after the ligature, theliver contained a great quantity of greengranulations, which were more numerous inthe left than in the right lobe. The cloacacontained green matter, as in the preced-ing case. If the animal lives forty hoursafterwards, the green colour of the liver andits excrements becomes more marked. Theselast experiments appeared to prove, that the